Fluid pressure control mechanism

ABSTRACT

In a fluid operated speed change mechanism the hydraulic pressure from a supply source is subjected to a pressure adjustment by a suitable control valve and is selectively supplied to a fluid motor which controls the engagement of a brake band in the planetary gearing. The reaction force caused by engagement of the brake band is transmitted mechanically or fluidically to the pressure adjusting control valve in a manner to increase the fluid pressure being supplied to the fluid motor thereby increasing the braking force of the brake band to prevent undue slippage. When the brake band is not applied, no reaction force can be transmitted to the control valve and the control valve will function in the normal manner.

United States Patent Murakami et al.

[54] FLUID PRESSURE CONTROL MECHANISM [72] Inventors: Noboru Murakaml;Kolchlro lliroznv/n,

both of Kariya, Japan Aisln Selkl Kabushiki Kaisha, Kariya Aichi Pref.,Japan 22 Filed: June 1,1970

21 Appl.No.: 42,420

[73] Assignee:

[30] Foreign Application Priority Date 1 June 27, 1972 v [56] ReferencesCited UNITED STATES PATENTS 3,251,245 5/1966 Foerster ..74/75l 3,251,2465/1966 Foerster et a1 ..74/75l 3,381,547 5/1968 Forster et al ..74 781Primary Examiner-Arthur T. McLeon Attorney-Sughrue, Rothwell, Mion, Zinn& Macpeak [57] ABSTRACT In a fluid operated speed change mechanism thehydraulic pressure from a supply source is subjected to a pressureadjustment by a suitable control valve and is selectively supplied to afluid motor which controls the engagement of a brake 1 band in theplanetary gearing. The reaction force caused by engagement of the brakeband is transmitted mechanically or fluidically to the pressureadjusting control valve in a manner to increase the fluid pressure beingsupplied to the fluid motor thereby increasing the braking force of thebrake band to prevent undue slippage. When the brake band is notapplied, no reaction force can be transmitted to the control valve andthe control valve will function in the normal manner.

4 Claims, 7 Drawing Figures PRESSURE 44 9 5B 82 R a 4 Q we I l I ,7 'i R2 47 5 4e 4e 49 wnessuns 89 uauuron VALVE PATENTEnJum m2 SHEET 10F 3FIG.

94 VALVE PRESSURE CONTROL MANUAL VALVE PRESSURE 9 REGULATOR VALVEPATENTEDJum I972 3. 672.243

sum ear 3 PRESSURE s n sr V CONTROL 5 A VALVE MANUAL VALVE 83 34PRESSURE REGULATOR VALVE FIG.5

FIG.4

FIRST SPEED STEP TRACTION FORCE SECOND SPEED STEP VEHICLE SPEED FLUIDPRESSURE CONTROL MECHANISM This invention relates to improvements in andrelating to a fluid pressure control mechanism, especially adapted foruse with a conventional automatic fluid-operated speed change mechanismfor powered vehicle.

In the conventional engageable unit contained in the automotivefluid-operated speed changer of the above kind, as an example, a brakeunit employed therein, the input force for the application of a brakeband to the cooperating brake drum is constant. However, in the case ofa powered vehicle fitted with an automatic speed changer of the abovekind, the traction force is reduced with increase of the vehicle runningspeed, as will be more specifically described hereinafter. It will beseen, therefore, the inputs to the various reaction members ofengageable units and of planetary gearings adapted for cooperation withpower-transmitting constituents of the automatic speed changer mustnaturally be kept at their respective constant levels, thus slips causedby an insufficient torque supply or unpleasant shocks caused by anexcess torque supply being frequently encountered.

It is therefore a main object of the present invention to provide animproved control mechanism of the kind above referred to capable ofmodulating the capacity of each of the engageable units contained in thehydraulically operated automatic speed changer in response to occasionalvariation of the transmitting drive torque.

A further object is to provide a control mechanism of the above kind,capable of substantially obviating conventional slips and shocks in theautomatic speed changer.

These and further objects, features and advantages of the invention willbecome more apparent when read the following detailed description ofseveral preferred embodiments of the invention by reference to theaccompanying drawings, in which:

FIG. I is a schematic explanatory representation of a fluidoperatedautomatic speed change mechanism to which the inventive fluid pressurecontrol mechanism cooperatingly fitted, said representation beingsubstantially sectional and a substantially upper half only of the wholearrangement being shown.

FIG. 2 is a connection diagram of the fluid pressure control mechanismaccording to this invention wherein, however, main constituents areshown in section.

FIG. 3 is a similar view to FIG. 2, illustrative of a preferred secondembodiment of the invention.

FIG. 4 is an explanatory diagram of the traction force of a poweredvehicle fitted with a fluid-operated automatic speed changer, beingplotted against the vehicle speed.

FIG. 5 is a similar view to FIG. 2, illustrative of a preferred thirdembodiment of the invention.

FIGS. 6 and 7 are sectional views of two modified hydraulic pressurecontrol valve employable in the present invention.

Referring now to the FIGS. 1 and 2 of the accompanying drawings, thepower transmission unit to be controlled by the mechanism according tothis invention is of the two-forward speed stage and one reverse speedstage standard type and shown in FIG. 1.

The numeral 10 represents a drive or input shaft which may preferably bethe crankshaft of a drive engine, not shown, of a powered vehicle onwhich the power transmission or automatic speed changer together withthe pressure control mechanism is fitted.

The numeral 17 and 29 are an intermediate shaft and an output shaft,respectively, all these shafts 10, 17 and 29 being arranged coaxiallyone after another. Although not specifically shown, all these shafts aremounted rotatably within a stationary housing 16 which is illustratedonly partly and in a highly simplified form.

Within the housing 16, a torque converter 11, a planetary gearing unit21, a clutch unit 18, a front brake 19 and a rear brake are provided.Torque converter 11 comprises a pump wheel 12, a turbine wheel 13 and astator wheel 14, as conventionally.

Pump wheel 12 is made rigid with the drive shaft 10; turbine wheel 13 isrigidly connected with intermediate shaft 17 and stator wheel 14 ismounted through one way clutch 15 on a first sleeve shaft 30 fixedlyattached to said housing 16. This kind of converter 11 is of theconventional design.

Planetary gearing unit 21 comprises a first sum gear 28, a second sungear 22, a ring gear 24, a plurality of longer planetary gears 23, aplurality of shorter planetary gears 27 and a carrier 26 mountingrotatably said planetary gears. First sun gear 28 is made rigid with theintermediate shaft 17, while second sun gear 22 is made rigid with asecond sleeve shaft 31 which is rotatably mounted on the intennediateshaft 17.

Sleeve shaft 31 is made rigid with drum 18a of clutch unit 18. Gearcarrier 26 is made integral with the driven or output shaft 29 andmounts in turn rotatably short planetary gears 27 and long planetarygears 23.

Ring gear 24 is formed on the drum 25 which is rotatably mounted on theoutput shaft 29.

Long gears 23 are kept in meshing with ring gear 24, second sun gear 22and short gears 27. Short gears 27 are kept in meshing with first sungear 28 and long gears 23.

Clutch 18 is so designed and arranged that second sun gear 22 rigid withdrum 18a, and first sun gear 28 are made integral with each other intoone rigid member. With the clutch 18 kept in its disengaged position,first sun gear 28 is driven by the intermediate shaft 17. On thecontrary, when the clutch is kept in its engaged position, both sungears 22 and 28 are driven simultaneously by the shaft 17.

Brake units 19 and 20 are arranged, when actuated, to apply brakingforce upon drums 18a and 25 for keeping second sun gear 22 and ring gear24 in their stationary position. These clutch and brake units 18, 19 and20 are all of the conventional design.

The power transmission shown in FIG. 1 provides, as was referred tohereinbefore, a forward low speed step, a forward high speed step and areverse drive step.

With clutch unit 18 and brake units 19 and 20 positioned all in theirdisengaged position, the transmission is in its neutral position and nodrive torque will be transmitted from the drive shaft 10 throughintermediate shaft 17 to the driven shaft 29.

When brake is applied to the drum 18a by the brake unit 19 so as tobring second sun gear 22 into its stationary position, the forward lowspeed drive step is realized. In this case, second sun gear 22 acts as areaction member in the planetary gear unit 21, and the drive torquetransmitted from the drive engine, not shown, through drive shaft 10 isfurther conveyed through torque converter 11, intermediate shaft 17,first sun gear 28, planetary gears 27; 23 and gear carrier 26 to thedriven shaft 29 which is mechanically connected through properconnection means to a drive wheel, not shown, adapted for drivingvehicle wheels, again not shown.

The forward high speed drive step is realized by bringing the clutch 18into engagement, while the brake units 19 and 20 are brought into intheir disengaged position. With the clutch 18 engaged, both sun gears 22and 28 are fixed, thus the constituent gears of the unit 21 beingbrought into solid to each other and a direct coupling condition betweenthe drive shaft 10 and the driven shaft 29 being thereby realized.

The rear drive step is realized by bringing the rear brake unit 20 intoits engaged position and by disengaging clutch unit 18 and front brakeunit 19.

Brake 20, when applied, acts to keep ring gear 24 in its stationaryposition so as to utilize it as a reaction. In this case, the forwarddrive torque supplied to first sun gear 28 is reversed by planetary gearunit 21, thus the gear carrier 26 and the driven shaft 29 being drivenin the opposite direction to the rotation of drive shaft 10.

Next, referring to FIG. 2, the pressure control mechanism according tothis invention will be described hereinbelow in detail.

The numeral 64 denotes a pump unit driven from the drive engine,although the connection means have been omitted from,the drawing onlyfor simplicity, said pump being connected through a conduit 71 to areservoir 32 and through a conduit 33 to ports 35 and 36 formed throughthe wall of a cylinder of a pressure adjusting valve unit 34.

The cylinder 40 receives slidably a valve member 39 which is formed witha pair of separated lands 37 and 38 having a common outside diameter.Between valve land 38 and the end of cylinder 40, there is inserted aspring 41 for urging the valve member 39 to move in the leftwarddirection in FIG. 2.

Ports 42 and 43 are kept in fluid communication with reservoir 32,although the connecting piping have been omitted from the drawing forsimplicity. Conduit 33 is fluidically connected with a port 46 which isbored laterally through the wall of cylinder of manual valve unit 44.

Manual valve 44 comprises a valve member 49 fitted with a pair ofseparated lands 47 and 48 and received slidably in the longitudinal boreof said cylinder 45. Ports 50 and 51 are bored laterally through thewall of cylinder 45, first port 50 being kept in fluid communicationthrough conduit 52 to a port 55 formed through the wall of cylinder 54of shift valve unit 53.

Port 51 fluidically communicated through a conduit 56 to branch conduits57 and 58, of which the first conduit 57 is kept in communication withport 59 of shift valve 53 and arranged to exert a hydraulic pressureupon the land at 61 of valve member which is slidable within thecylinder 64 of valve unit 53. Conduit 58 is dept in communicationthrough conduit to the hydraulic working chamber at 72 of front brakeunit 19, and through branch conduits 73 and 74 respectively to ports 77and 78 formed in the cylinder at 76 of a hydraulic pressure controlvalve unit 75. The numeral 65 represents a land 65 formed on valvemember 60 which is urged to move leftwards in FIG. 2 under the springforce at 67. This spring 67 is inserted between the valve land 65 andthe cylinder end at 66.

Ports 68 and 69 are discharge ports kept in fluid communication with thereservoir 32, although the communication means have been omitted fromthe drawing only for simplicity.

Hydraulic working chamber 80 of rear brake unit 20 is fluidicallyconnected through a conduit 81 to a port 82 which is formed in thecylinder 45 of manual valve unit 44. The numeral 83 represents areaction chamber which receives the reaction force developed in thefront brake unit 19, said chamber 83 being kept in fluid communicationthrough conduits 84 and 85 to a port 86 formed in the valve unit 76. Thechamber 83 is fluidically connected through conduit 87 to a smallchamber 88 formed in the pressure regulator valve unit 34. Into thissmall chamber 88, the reduced end at 89 of the valve member 39 of thevalve unit 34 project, so as to receive the hydraulic pressure of valveunit 34. Fluid pressure control valve unit 75 comprises a valve member90 axially slidable in a cylinder 76 of the unit 75, said valve memberbeing formed with a pair of separated lands 91 and 92.

Valve member 90 is urged constantly to move leftwards in FIG. 2 underthe influence by a spring inserted between valve land 92 and cylinderend 93. A discharge port 95 is provided which is kept in fluidcommunication with the reservoir 32, although the communication meanshave been omitted from the drawing only for simplicity.

The operation of the mechanism as shown and described is as follows.

Now assuming that the various valve units are positioned in their normalposition shown, with the valve member 49 of manual valve unit 44positioned at 2-range position. The hydraulic pressure supplied by pump64 is conveyed through conduits 35 and 36 to a ring space 96 formedbetween valve lands 37 and 38 and to the left side of land 37.

With increase of the delivery pressure from pump 64 and the hydraulicpressure acting upon the left side surface of valve land 37 becomeslarger than the spring pressure at 41, the valve member being shiftedrightwards. With rightward shift of valve land 38, the chamber 96 beingbrought into fluid communication with the discharge port 42. Withdecrease of the hydraulic pressure acting upon the left hand side ofland 37, the valve member is shifted under predominant influence ofspring pressure at 41, the land 38 interrupts the communication betweenthe ports 35 and 42. In this way, the delivery pressure from pump 64will be kept at a certain constant valve.

In this way, an adjusted oil pressure to a certain constant level issupplied to the port 46 of manual valve 44, the pressure oil beingconveyed through port 50, conduit 52, ports 55 and 62 and conduit 63 toclutch 18 which is thus actuated for the realization of the forward highspeed drive step.

When the manual valve 44 is shifted to l-posidon" by manipulating aproper manual means such as accelerator pedal, the valve member 49 willbe shifted leftwards, until the land 47 is brought into opposition tothe cylinder part 97 and the left end of land 48 is brought intoregistration with the right-hand end of port 46. Under these operatingconditions, the constant oil pressure delivered from pump 64 throughpressure regulator valve unit 34 is conveyed further through conduit 33,ports 46; 50 and conduit 52 to port 55, and at the same time, throughport 51, conduits 56 and 57 to port 59. Upon application of this oilpressure to port 59, valve member 60 will be shifted to the rightagainst the spring force at 67, and the port 44 is interrupted by theend of land 61 for interrupting the pressure oil supply to the clutch18, while oil pressure is supplied through conduits 56, 58 and 70 to thehydraulic working chamber 72 of brake unit 19.

At the same time, hydraulic pressure is supplied from conduits 73 and 74to the both sides of land 91 formed on the valve member 90 of valve unit75, the hydraulic pressure acting upon the left-hand surface of valveland 91 acts upon valve member 90 against spring action 94 so as to movethe member rightwards for interrupting the already established hydrauliccommunication between port 74 with the hydraulic chamber of front brakeunit 19. During inactivation of the front brake unit 19, ports 86 and 78are kept in fluid communication with each other, and the pressure oilprevailing between port 88 and reaction chamber 83 is returned throughconduit 56 and port 51 to reservoir 32, thereby no hydraulic pressureacts upon the reduced end 89 of valve member 39 of pressure adjustingvalve unit 34. Even when fluid communication between port 86 and 78should be kept in interruption, the residual hydraulic pressureprevailing between port 88 and reaction chamber 83 will do for thedesired purpose, if it does not adversely affect upon the pressureadjusting valve 34 during the non-applied position of the front brakeunit 19.

When the hydraulic pressure is supplied to the supply chamber 72 offront brake 19, the latter i s thereby caused to actuate and a reactionoil pressure in relation to the braking torque is conveyed from reactionchamber 83 through conduits 84; 87 to small chamber 88 in which thereduced end part 89 of pressure regulator valve 34 projects and,therefore, the latter is hydraulically urged. The reaction oil pressureacting upon the reduced valve end acts, being assisted by the springforce 41, upon the valve member 39 leftwards in FIG. 2. Therefore, theoil pressure subjected to adjustment by the valve 34 becomes higher thanbefore, and is supplied to the supply chamber 72 of front brake unit 19.In this way, the reaction pressure is modified in accordance withoccasional variation in the torque transmitted from the drum 18a offront brake 19. Therefore, the oil pressure adjusted by the valve unit34 will vary with the torque as supplied.

The second embodiment of the invention is shown in FIG. 3. Substantialconstituent parts of the present embodiment are similar to thoseemployed in the foregoing first embodiments. For easy identification andcomparison purpose, these similar parts are denoted respective samereference numerals as be fore.

The main structural difference of the present embodiment from the secondone resides in the following.

Conduit 99 is connected at its one end with conduit 58, while theopposite end of conduit 99 is fluidically connected with a port 100which is formed in the pressure adjusting valve unit 34. Morespecifically, the port 100 is provided between discharge port 43 andport 88, valve land 101 formed on valve member 39 is arranged to beslidable between ports 88 and 100 and within the longitudinal bore ofcylinder 40.

The operation of this second embodiment is as follows:

With the manual valve 44 manipulated to l-position" wherein variousvalve units are positioned as shown in FIG. 3, pressure oil deliveredfrom pump 64 is subjected to adjustment by pressure adjusting valve 34and then fed to the port 46 of manual valve 44. The pressure oil fed toport 46 is conveyed through port 51, conduits 56; 57 to the left-handside surface of the land 61 on valve member 60, so as to urgehydraulically the latter to move rightwards for interrupt the oilpassage from port 50 to clutch 18.

Pressure oil in conduit 56 is supplied through conduits 58; 70 to supplychamber 72 of front brake unit 19 for actuation thereof, and it will beconveyed through duct 73 and act upon the left side surface of valveland 91 formed on valve member 90 in the hydraulic pressure controlvalve unit 75, for hydraulically urging the valve member to sliderightwards, so as to interrupt the fluid communication between ports 78and 86. On the other hand, pressure oil is conveyed from conduit 58 toport 100 of adjuster valve unit 34, the hydraulic pressure thus actingupon the left-hand side surface of valve land 101 on valve member 39 andsaid hydraulic pressure being equivalent to that now prevailing in thebrake unit 19. Upon the righthand side surface of valve land 101, thepressure oil from the reaction chamber 83 of brake unit 19 will act,and, indeed, through the intermediary of conduits 84, 87 and port 88.

In the engageable unit, for instance, a brake unit as its representativeexample, the acting force or impact force F,, and reaction force F maybe defined by the following formula T= (F F ,,)R where,

T stands for the torque applied to the brake hand; or friction torqueacting between brake hand and brake drum;

R stands for the radius of the brake drum; therefore,

F T/R F, The reaction equals to the input plus T/R.

From the above Formula l F, is larger than F and thus, a oil pressure FF will act upon the right-hand side surface of valve land 101 so as tourge the valve member to move leftwards and this urging action isassisted by the spring force at 41. Therefore, pressure oil will beconveyed through port 36 to port 46 and the oil pressure will beadjusted to a higher level by the reaction input acting upon the bothside surfaces of valve land 101.

A third embodiment of the invention is shown in FIG. 5 of theaccompanying drawing.

64 represents a pump which communicates through conduit 71 to reservoir32. On the other hand, the pump 64 communicates through conduit 33 toport 35 bored laterally through the cylinder 40 of pressure regulatorvalve 34. Valve unit 34 comprises valve member 39 which is formed withland 38 having a common outside diameter, said valve member beingslidably received within the longitudinal bore of the cylinder 40. Acompression spring 41 is inserted between valve land 38 and thecorresponding cylinder end, so as to urge the valve member 39 to moveleftwards in FIG. 5. 42 and 43 represent discharge ports communicatingwith the reservoir 32. Conduit 33 is kept in fluid communication withport 46 formed in the wall of cylinder 45 of manual valve unit 44.

Manual valve 44 comprises a valve member 49 formed with lands 47 and 48,said valve member being received slidably in the cylinder 45. Ports 50and 51 are formed in the cylinder 45. Port 50 communicates throughconduit 52 to port 55 formed in the cylinder 54 of shift valve 53. Itcommunicates further through port 62 and conduit 63 to the supply sideof clutch unit 18. Port 51 is connected through conduit 56 to twobranches 57 and 58. Conduit branch 57 communicates with port 59 so as toimpress hydraulic pressure upon the land 61 on valve spool 60 which isslidably received in the cylinder 54 of shift valve unit 53. Thehydraulic pressure will be conveyed through conduit 58 to the supplychamber 72 of front brake unit 19. A land 65 is formed on shift valve 60subjected to an urging force exerted by a spring 67 inserted betweensaid land and cylinder end wall 66. Ports 68 and 69 are provided fordischarge purpose to the reservoir 32.

Supply chamber is kept in fluid communication through conduit 81 withport 82 formed in the cylinder 45 of manual valve 44.

Numeral 149 is a strut adapted for receiving brake reaction in frontbrake unit 19 and acts to brake the drum 18a by the actuation of frontbrake unit 19 when hydraulic pressure prevails in the supply chamber 72.At this stage, the strut 149 is subjected to a reaction F, in responseto the braking torque. Strut 149 is mounted on a lever pivoted on alever pin 141 which is fixedly mounted on a stationary casing, notshown. The strut will act upon lever 140 so as to rotate the latter forurging valve member 139 of valve unit 34 towards left by cooperationwith spring 41. By this pressure adjusting operation, the relatedhydraulic pressure will be adjusted to a higher level.

The adjusted hydraulic pressure will be fed to the supply chamber 72 offront brake unit 19, and since the reaction force is modulated inresponse to the torque received by the front brake 19 from the drum 18a,the hydraulic pressure subjected to adjustment by the valve unit 34 willvary with variation of the torque transmitted.

In the foregoing description, all the embodiments have been arranged soas to control the acting force or input force to the front brake unit.Similar control may naturally performed on other brake unit by providingsimilar arrangement therefor. It

is also possible to control the hydraulic pressure in the aforementionedway in the engageable means of a three forward speed type automatic oreven manual speed changer of the fluid operated type.

An example of the variation of the traction force of the fluid-operatedautomatic speed changer is seen in the chart shown in FIG. 4 which hasbeen plotted against the vehicle speed. It is self-explanatory andserves for better understand ing of the nature of function of theinventive pressure control mechanism according to this invention.

In the valve arrangement shown in FIG. 6, disadvantageous oscillativemovement of a pressure regulator valve can be obviated substantially. Asimilar representation shown in FIG. 7 illustrates a conventionalcomparative one.

Numeral 210 shown schematically a valve housing which is provided with alongitudinal bore 211 in which a valve member 212 is received slidably.

Valve housing 210 is formed with ports 222, 225 and 226 which are keptin fluid communication with the valve bore 2 1 1.

Within the valve bore 211, two separated oil chambers 218 and 221 areformed by said valve member. A spring 227 is provided within oil chamber221 for urging the valve member to move leftwards in FIG. 6. Numeral 228denotes pump which sucks oil through suction pipe 241 from an oilreservoir 244. The sucked oil is delivered from the pump to a dischargepipe 39 which communicates with a port 222 of said oil chamber 218through a conduit 232. Port 225 is kept in fluid communication throughconduits 238 and 240 to the reservoir 244.

Port 226 is connected through conduit 239 provided midway with anorifice 233, said conduit being hydraulically connected to a furtherconduit 240. Discharge conduit 230 is connected to an outlet conduit231. The pressure-adjusted oil is connected to any of the foregoinghydraulic circuits corresponding to respective embodiments for supply ofcontrolled pressure oil.

The pressure control mechanism 250 is positioned at a lower level thanthe oil level in the reservoir 244.

In this prior mechanism, a ring groove 317 is formed midway on the valvespool 312 by the provision of two separated lands 313 and 315. A ringspace 320 kept in fluid communication with the interior of said ringgroove 317 is specifically provided in this valve unit. A conduit 335 isfurther provided which is hydraulically connected with discharge conduit330, on the one hand, and with said ring space 320, on the other hand.

Similar arrangement shown in FIG. 7 represents a comparativeconventional arrangement. Similar parts of this prior mechanism as thoseof that shown in FIG. 6 are denoted with respective same referencenumerals each added with 100 for easy identification and comparison.

Conduit 332 which connects end chamber 318 with delivery conduit 331 isformed midway with an orifice 333, while the conduit 339 connecting thechamber 321 to discharge conduit 340 leading to the reservoir 314 isfitted with no orifice means.

The operation of the pressure control valve mechanism shown in FIG. 6will be described hereinbelow in comparison with that of theconventional one shown in FIG. 7.

Pump 228 or 328 sucks oil from reservoir 244 or 344 and delivers apressurized oil flow through conduits 230 or 330 and 232 or 332 to thechamber 218 or 318. The thus supplied oil pressure to the last-mentionedchamber will act upon the valve spool 212 or 312 against the action ofspring 227 or 327 so as to urge the spool to move rightwards in FIG. 6or 7. When this hydraulic urging pressure overcomes the counter springaction, the spool will shift rightwards, until discharge port 225 or 325is opened for bringing the chamber 218 or 318 and discharge conduit 238or 338 into fluid communication with each other, so as to reduce the oilpressure in the chamber 218 or 318.

With the thus reduced oil pressure, spring pressure at 227 or 327 willbecome predominant for urging the valve spool to move leftwards, untilthe fluid communication between the port 225 or 325 and the chamber 218or 318 is interrupted. At the last moment, the spring pressure willbecome in balancedout condition with the hydraulic urging force, so asto set the oil pressure in the conduit 230 or 330 to a certain desiredlevel, as determined by the thus occasionally invited spring pressure.The thus adjusted oil pressure by the pressure control valve 250 or 350may be utilized as the line pressure referred to hereinbefore inconnection with FIGS. 1, 2, 3 and 5.

When the valve unit 250 or 350 acts to set in the above mentioned waythe variable line pressure, substantial oscillation of the valve spoolwill be frequently and disadvantageous invited.

By the provision of the orifice 233 or 333, thereby providing ahydraulic damping force for suppressing the disadvantageous valveoscillation will be provided. In the arrangement proposed by theinvention, the damping orifice is provided in the discharge pipingsystem leading from the discharge port 226 to the reservoir 244, inplace of the delivery piping leading from the delivery side of pump 328to inlet port 324.

For the realization of this damping purpose, the provision of land 315was necessary according to the prior art, in addition to the provisionof the chamber 320, conduit 335 and the like. According to the novelarrangement, the pressure control unit may well be dispensed with theseadditional parts which simplifies substantially the whole valvestructure.

The embodiments of the invention in which an exclusive property orprivilege is claimed are as follows:

1. A pressure control device for a hydraulic fluid operated speed changemechanism utilizing a transmission gear set and various frictionengaging devices for effectuating various gear ratio linkages in a powertrain comprising:

a reservoir for the hydraulic fluid;

a pump connected to the reservoir;

control means for regulating the desired gear ratio linkages andreceiving hydraulic fluid under pressure from the P p; at least onehydraulic force device connected to the control means for actuating afriction engaging device; a reaction member means connecte to thefriction device for producing a signal proportional to the reactionforce generated by the engagement of the friction engaging device, and

pressure adjusting valve means for regulating the pressurized hydraulicfluid supplied to the control means in response to the signal generatedby the reaction member means by metering the hydraulic fluid to thereservoir, whereby sudden shocks from insufiicient or excessive torqueto the friction engaging devices are prevented.

2. A pressure control device as in claim 1, where the pressure adjustingvalve means includes a valve spool and a cylinder, one side of the valvespool connected to the hydraulic force device for generating one force,while the other side is connected to the reaction member means forgenerating an opposing force, whereby the resultant of the forcescontrols the metering of the hydraulic fluid to the reservoir.

3. A pressure control device as in claim 1, where the reaction membermeans includes a strut and a carnming lever for transmitting a force tothe pressure adjusting valve means, the pressure adjusting valve meansfurther including a cylinder, a metering valve spool mounted in thecylinder and a conduit having a restrictive orifice for supplyingmetered hydraulic fluid to the same side of the valve spool as thecamming lever force whereby oscillations of the metering valve spoolwill be damped.

4. A fluid operated speed changer for a vehicle comprising:

a planetary gearing means for providing speed reductions;

a reservoir of hydraulic fluid;

a pump means connected to the reservoir;

a pressure regulator valve means for distributing hydraulic fluid fromthe pump means, and

engagement control means for controlling the actuation of the planetarygearing means including an input means, a reaction means, and a fluidpressure control means provided between said input and reaction meansfor connecting said pressure regulator valve so as to actuate saidreaction means in the pressure increasing direction of said pressureregulator valve in case of energization of said input means, and forinterrupting the cooperating conditions of said reaction means and saidpressure re gulator valve in case of failure of fluid pressure to beconveyed to said input means.

1. A pressure control device for a hydraulic fluid operated speed changemechanism utilizing a transmission gear set and various frictionengaging devices for effectuating various gear ratio linkages in a powertrain comprising: a reservoir for the hydraulic fluid; a pump connectedto the reservoir; control means for regulating the desired gear ratiolinkages and receiving hydraulic fluid under pressure from the pump; atleast one hydraulic force device connected to the control means foractuating a friction engaging device; a reaction member means connectedto the friction device for producing a signal proportional to thereaction force generated by the engagement of the friction engagingdevice, and pressure adjusting valve means for regulating thepressurized hydraulic fluid supplied to the control means in response tothe signal generated by the reaction member means by metering thehydraulic fluid to the reservoir, whereby sudden shocks frominsufficient or excessive torque to the friction engaging devices areprevented.
 2. A pressure control device as in claim 1, where thepressure adjusting valve means includes a valve spool and a cylinder,one side of the valve spool connected to the hydraulic force device forgenerating one force, while the other side is connected to the reactionmember means for generating an opposing force, whereby the resultant ofthe forces controls the metering of the hydraulic fluid to thereservoir.
 3. A pressure control device as in claim 1, where thereaction member means includes a strut and a camming lever fortransmitting a force to the pressure adjusting valve means, the pressureadjusting valve means further including a cylinder, a metering valvespool mounted in the cylinder and a conduit having a restrictive orificefor supplying metered hydraulic fluid to the same side of the valvespool as the camming lever force whereby oscillations of the meteringvalve spool will be damped.
 4. A fluid operated speed changer for avehicle comprising: a planetary gearing means for providing speedreductions; a reservoir of hydraulic fluid; a pump means connected tothe reservoir; a pressure regulator valve means for distributinghydraulic fluid from the pump means, and engagement control means forcontrolling the actuation of The planetary gearing means including aninput means, a reaction means, and a fluid pressure control meansprovided between said input and reaction means for connecting saidpressure regulator valve so as to actuate said reaction means in thepressure increasing direction of said pressure regulator valve in caseof energization of said input means, and for interrupting thecooperating conditions of said reaction means and said pressureregulator valve in case of failure of fluid pressure to be conveyed tosaid input means.